Fishing – trapping – and vermin destroying – Fishing – Nets
Patent
1998-11-09
2000-10-17
Carone, Michael J.
Fishing, trapping, and vermin destroying
Fishing
Nets
A01K 73045
Patent
active
061313270
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to an otter board.
Otter boards are especially used for expanding a trawl, whereby two symmetrical otter boards are connected to respective side portions of a trawl, and whereby the otter boards are connected between the trawling vessel and the trawl by means of cables.
Such an otter board is known from GB-A-2 161 351 and comprises a number of transversly mounted elongate hydrofoil means, whereby each hydrofoil means comprises either one blade or a pair of blades, and whereby the hydrofoil means are spaced apart and distributed longitudinally in the direction of the water flow in a mounting frame comprising two straight, elongate mounting members being parallel to one another. The respective hydrofoils or each pair of hydrofoils are arranged in such a way that the cords are offset in relation to the mounting frame and in such a way that the offset angles are larger for a leading hydrofoil means compared to a trailing hydrofoil means.
In one embodiment, where the hydrofoils are arranged in pairs, each hydrofoil means comprises an overlapping upper or leading blade and a narrower lower or trailing blade, thereby forming channels or slots between each pair of foils.
The document GB-A-2 161 351 shows an embodiment having five pairs of hydrofoils being arranged in the mounting frame.
On the underside of the otter board there is provided a bracket having a number of fixture points for the attachment of cables to the trawler and on the mounting frame there is provided attachment points for the trawl. By means of these fixture points the function of the otter board, including the angle of attack of the board, can be adjusted.
The above board is both suited for operation near the sea-bottom and in mid-waters.
Prior art document DE-A-0 562 243 shows an otter board comprising a number of transversly mounted, elongate hydrofoils being longitudinally spaced apart in a mounting frame, and being arranged in such a way that the trailing edge of a hydrofoil and the leading edge of a neighbouring hydrofoil is situated next to each other. The hydrofoils are arranged in such a way that a leading hydrofoil is more offset to the frame than a trailing hydrofoil, and so that the plurality of hydrofoils, from a side view, altogether describe a shape like a wing profile.
OBJECTS OF THE INVENTION
The lateral directed force or lift force, which is generated by means of the otter boards mentioned above, is accomplished by means of the force generated by a curved hydrofoil profile, when exposed to a passing flow of water, whereby under-pressure or vacuum appears at the top side of the curved hydrofoil and over-pressure is generated on the underside of the hydrofoil, analogous with the forces generated by an aeroplane wingfoil, wherein the velocity of flow of air is higher and the pressure lower on the top side than on the underside of the airfoil.
As it is known in the field of airfoils, when the angle of attack for a foil is increased the under-pressure on the top side and the pressure on the underside of the foil increase. The surface friction or the drag, however, increases abruptly at a certain higher, critical angle of attack where the flow alters from being laminar to being turbulent. At this point the drag coefficient increases sharply.
Normally, otter-boards are angled even higher than the above mentioned critical angle for maximizing the pressure on the underside of the board during operation. Thus, attempts have been made in the prior art to improve the dynamics of otter boards in terms of spreading efficiency, drag and stability for high angles of attack. However, it is found that these qualities have still not been fully achieved in the prior art.
Therefore, it is a primary object of the present invention to increase the effective area of under-pressure or vacuum for an otter board construction of a given size without increasing the surface friction over a broad range of angles of attack of the otter board.
It is a secondary object of the present invention to pro
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patent: 4640037 (1987-02-01), Ashworth
patent: 4653213 (1987-03-01), May
patent: 4879830 (1989-11-01), Quick
patent: 5265367 (1993-11-01), Kinoshita
patent: 5267408 (1993-12-01), Kinoshita
patent: 5283972 (1994-02-01), Kinoshita
Ark Darren W.
Carone Michael J.
Sapone, Esq. William J.
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